The present invention relates to a method and composition for applying reflective markings on highways, roadways and the like in which the paint composition is applied at ambient temperature without the use of external heating means. A relatively fast dry time is obtained, generally of the order of about 20-60 seconds or less.
There are several procedures which have been used in the past for marking highways, their object being to apply a suitable marking material without the use of barriers, cones, traffic-deflecting means or the like such that the applied coating composition dries rather rapidly and preferably within a time period of one to two minutes or less. One such technique that has gained wide acceptance is described in U.S. Pat. No. 3,474,057. In that patent extremely fast dry times of road marking materials is achieved with the use of heat; that is, the paint composition is heated in a closed system to a temperature of 140.degree.-250.degree. F., then released from the closed system and sprayed onto the road surface in order to mark the road surface and permit the paint to dry quite rapidly, generally in less than about one minute or less.
While heating road marking paints and compositions, such as those mentioned above, has met with substantial commercial application, it is necessary to use rather elaborate equipment, which must be portable, and requires not only maintenance during operation but also the use of a separate heat source for raising the heat of the road marking composition carried by the equipment.
Other road marking compositions and procedures are described in U.S. Pat. Nos. 3,046,851, 3,136,733 and 3,321,329. While the paint compositions described in these patents are applied without the use of heat, the dry time required to obtain a suitable marking line which can be traversed by vehicles and road traffic is at least greater than one minute, and generally of the order of about three minutes or more. Such compositions usually require the use of road marking cones and the like to direct traffic away from the wet composition until a suitable non-tracking film has formed on the marked road surface.
Other prior procedures have used drop-on glass spheres, sand, particulate matter or the like in order to reduce the drying time of the applied paint composition. An example of this is a rounded sand such as crystal grade silica sand in a mixture ratio of one part glass spheres to two parts round sand. Using spheres or mineral matter in such a procedure, when applied to a wet film on the highway surface the close packing of the spheres which are subsequently applied provides a surface which is free from wet paint composition on the upper surface, yet it is rather immobile due to the solvent loss occurred in spraying. The glass-mineral surface is sufficient to support the tires of an automobile passing over the marked surface without touching the wet paint composition below the glass-mineral coating.
Other prior art procedures, including directing the projected paint spray through an open flame, are described in U.S. Pat. No. 3,321,329, or heating the surface of the road itself as described in U.S. Pat. No. 3,410,185.